Field of the Invention
This invention relates to injection molding apparatus for the injection molding of shoe soles, and more particularly, to an apparatus for facilitating the manufacture of shoe soles having two or more layers, preferably of polyurethane.
The present invention is especially applicable in connection with problems involved in working with polyurethane. This material causes difficulties, above all, because the raw material is placed into the mold cavity in more or less liquid form by pouring or spraying, and the material is hardened within the mold while expanding. This calls for special attention to be placed on the sealing of the mold cavities.
Various designs of injection molding molds for the manufacture of two-layer shoe soles while molding them to the shoe upper simultaneously are in existence. In such molding processes, either the inner sole layer facing the upper can be molded first and fastened to the upper, and then the outer sole layer may be fashioned thereon, or else it is possible to mold the sole layers in reverse order. The latter procedure is employed especially when working with polyurethane.
The injection molding apparatus for working with plastics such as polyvinyl chloride which have been developed in practice in this technical field are not necessarily also suitable when working with polyurethane. However, developments in the shoe industry have been characterized by an increasing use of polyurethane. Consequently, a major concern in producing the present invention is to propose measures by means of which the equipment already on hand for working with polyvinyl chloride may be converted into apparatus suitable for working with polyurethane.
The basic task in producing the present invention is to propose a casting or injection molding apparatus of such a nature that it may be installed on equipment that is already on hand, at slight expense in making of the conversion and for the special purpose of working with polyurethane.
In order to best be able to perform this function, the apparatus of the present invention is equipped with at least two bottom stamps, each stamp being attached to a separate supporting arm, which are directed towards each other at an angle, specifically at right angles, and which intersect each other at a common swinging support. In this way, supporting arms form a rigid angle piece to the respective ends of which the bottom stamps are fastened. By swinging the angle piece through an angle of 90.degree., for example, about a horizontal pivot axis, the bottom stamps may be lined up with the other parts of the mold alternately. The angle piece, with the bottom stamps attached to it, may also be raised and lowered by a pressure medium cylinder acting through the pivot axis of the swinging angle piece.
The unit consisting of the bottom stamps, the angle piece, and the pivotable or swinging support may be installed in the present invention on a casting or injection molding apparatus as a single piece of equipment, preferably on the outer edge of one of the molding apparatus rotary attachments. The pressure medium cylinder and motor for driving the angle piece in rotation also properly belongs to this unit. In conformity with another proposal included in this invention, the unit may be held together by a supporting frame which is shaped like a partially open box. On the upper side of the box, the parts of the side mold may be moved laterally, while the upper mold formed by the last with the shoe upper, remains a part of the existing installation in the normal way.
It is another object of the present invention to provide a special construction of the mold, that is, of the bottom stamps that are employed in connection with the side mold to define partially the mold cavities. The bottom stamps have edge ridges running around them, and as a result, the bottom stamps take the shape of containers, shallow dishes or similar receptacles that are open at the top. The edge ridges work together with an appropriately designed projection of the side mold to form a seal and in the mold pouring position the edge ridges effect the seal with that side mold projection.
Further details of the invention are given in the following description with references to the numered parts shown on the attached diagrams included.